Macromolecules in urine have been implicated in protection against nephrolithiasis. Protective (inhibitory) effects of human urinary macromolecules on the crystallization of calcium oxalate were found when these urinary macromolecules were added to water or salt solutions, which mimicked human urine with respect to the concentrations of the most abundant small MW species. The aspects of calcium oxalate crystallization affected by urinary macromolecules were an inhibition of nucleation (increased metastable limit), an inhibition of the crystallization rate, a decrease in the supersaturation level and a decrease in adhesion of crystals to container surfaces.